• Mikael Pettersson's avatar
    m68k: implement futex.h to support userspace robust futexes and PI mutexes · e4f2dfbb
    Mikael Pettersson authored
    Linux/M68K currently doesn't support robust futexes or PI mutexes.
    The problem is that the futex code needs to perform certain ops
    (cmpxchg, set, add, or, andn, xor) atomically on user-space
    addresses, and M68K's lack of a futex.h causes those operations
    to be unsupported and disabled.
    
    This patch adds that support, but only for uniprocessor machines,
    which is adequate for M68K.  For UP it's enough to disable preemption
    to ensure mutual exclusion (futexes don't need to care about other
    hardware agents), and the mandatory pagefault_disable() does just that.
    
    This patch is closely based on the one I co-wrote for UP ARM back
    in August 2008.  The main change is that this patch uses the C
    get_user/put_user accessors instead of inline assembly code with
    exception table fixups.
    
    For non-MMU machines the new futex.h simply redirects to the generic
    futex.h, so there is no functional change for them.
    
    Tested on aranym with the glibc-2.17 test suite: no regressions, and
    a number of mutex/condvar test cases went from failing to succeeding
    (tst-mutexpi{5,5a,6,9}, tst-cond2[45], tst-robust[1-9], tst-robustpi[1-8]).
    Also tested with glibc-2.18 HEAD and a local glibc patch to enable PI
    mutexes: no regressions.
    Signed-off-by: default avatarMikael Pettersson <mikpe@it.uu.se>
    Acked-by: default avatarAndreas Schwab <schwab@linux-m68k.org>
    [geert: Added removal of ""generic-y += futex.h"]
    Signed-off-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
    e4f2dfbb
futex.h 1.9 KB